n 1 : the division of the human body that contains the brain, the eyes, the ears, the nose, and the mouth : also : the corresponding anterior division of the body of various animals including all vertebrates, most arthropods, and many mollusks and worms 2 : HEADACHE 3 : a projection or extremity esp. of an anatomical part: as a : the rounded proximal end of a long bone (as the humerus) b : the end of a muscle nearest the origin c : the anterior end of an invertebrate : SCOLEX 4 : the part of a boil, pimple, or abscess at which it is likely to break 5 : the end of a lipid molecule that consists of a polar group and is regarded as being opposite to the tail headadj